397 



valve is expressly adapted to the production of an effect of this kind, 

 in various degrees, corresponding with the respective characters and 

 habits of each tribe. He is thus led to conclude that the function 

 which the tricuspid valve exercises exhibits, in the extent of its de- 

 velopement, a regular gradation, when followed throughout the dif- 

 ferent orders of Mammalia and Birds,- and that it extends even to 

 some Reptiles. 



The force with which the circulating blood is impelled by the ge- 

 neral venous trunks into the heart, and which is dependent on the 

 action of the arterial system, the degree of compression arising from 

 muscular action^ combined with the resistance of the valves of the 

 veins, and is also influenced by occasional accumulations of blood 

 from rapid absorption, from impeded respiration, and from cold applied 

 to the surface of the body, is shown to be subject to great and sud- 

 den variations. Any increase taking place in this force tends to pro- 

 duce distension of the right ventricle of the heart, followed by dis- 

 turbance in the valvular action of the tricuspid membrane, owing to 

 the displacement of its parts, which thus allows of a considerable re- 

 flux of blood into the auricle. Among the Mammalia, the lowest degree 

 of this action, corresponding to that of a safety-valve, is found in the 

 rodent, the marsupial, and the canine tribes. The next in degree is 

 that which occurs in the order of Edentata and the feline genus. The 

 Quadrumana occupy the next place in the scale of gradation. The 

 human conformation exhibits this function in a very conspicuous man- 

 ner, especially in the adult period ; for at birth, when the right ventricle 

 is unyielding, it scarcely exists ; and in various states of disease the tri- 

 cuspid valve acts with too much or with too little efficacy. The Pachy- 

 dermata and Ruminantia come next in succession. The Seal exhibits 

 this peculiarity in a still higher degree , but in no order of Mammalia 

 does it exist to so great an extent as in the Cetacea, which appear, 

 indeed, to possess a peculiar additional provision for effectually se- 

 curing the permanent performance of this office, which the author 

 compares to that of a safety-valve. A similar function, subject to si- 

 milar gradations, is likewise traced in different orders of Birds. It is 

 but slight in the Gallinaceae 5 and rather greater in the predaceous 

 tribes. In some of the Waders it exists to a considerable extent ; but 

 is greatest of all in the orders of Passerines and Scansores. Crocodiles 

 and the Ornithorhynchus present some traces of this peculiar provi- 

 sion relatively to the circulation. 



" Some Account of the appearances of the Solar Spots, as seen 

 from Hereford, on the 15th and 16th of May, 1836, during and after 

 the Solar Eclipse." By Henry Lawson, Esq., in a Letter to Sir 

 Henry Ellis, K.G.H., F.R.S., by whom it was communicated to the 

 Society. 



The spots on the sun's disc, at the period referred to, were very 

 numerous ; and one of great size, being many thousand miles in dia- 

 meter, in particular attracted attention, from its penumbra presenting 

 an appearance similar to a sky filled with small flocculent white clouds, 

 perfectly distinct from one another 5 while on two sides were seen 



